Thermal cell

ABSTRACT

An improved device in the form of a web for detecting fires and other high temperature conditions comprises a conductive ring with a number of filamentary thermal cells mounted thereon, each cell including a core comprising stainless steel with a glass coating of specific composition disposed on the core and ionically conductive at a certain temperature. A sheath of metal, such as silver, dissimilar to the core metal is disposed on the glass coating. A lattice form of a spaced plurality of intersection cells connected at opposite ends to the ring and interwoven with one another at the intersections is provided.

United States Patent Primary Examiner-John W. Caldwell AssistantExaminer-Scott F. Partridge Attorney-Donald R. Nist ABSTRACT: Animproved device in the form of a web for'detecting tires and other hightemperature conditions comprises a conductive ring with a number offilamentary thennal cells mounted thereon, each cell including a corecomprising stain less steel with a glass coating of specific compositiondisposed on the core and ionically conductive at a certain temperature.A sheath of metal, such as silver, dissimilar to the core metal isdisposed on the glass coating. A lattice form of a spaced plurality ofintersection cells connected at opposite ends to the ring and interwovenwith one another at the intersections is provided.

1 THERMAL can.

This application is a divisional application of application SerfNo.475,022, now U.S. Pat. No. 3,4l6,97l, filed July 26, 1965.

This invention relates to energy conversion and more particularlyrelates to a thermally activated battery configuration in the form of afiber and systemsincorporating the same.

There are many instances where a device that converts thermal energy toelectrical energy is useful. For example, such a device is ideal as asensor for detecting fires or other high temperature conditions.Currently, thermistors or thermocouples are often used for this purpose.The use of thermistors requires a power source with a relativelyconstant output characteristic and are subject to failure as a result ofrough handling or exposure to moisture. Thermocouples eliminate the needfor an external power supply but have very small power outputs and arealso relatively fragile.

According to the present invention, a thermally activated cell isprovided that is so sturdy that it itself can be used to add strength toa structure in which it is incorporated. It can be constructed in almostany geometric configuration and in such a manner as to produce asubstantial power output. Since the device generates energy only whenheated, freedom from false alarms is inherent in its use.

The thermal cell of the present invention basically consists of afilament having a metallic core, a coating of a suitable glasscomposition on the core, and a coating of a second metal deposited overthe glass coating. Heating such a structure to within the designedoperating temperature range results in the glass serving as anelectrolyte between the two metal electrodes and causes electricalenergy to be produced. The devices or cells can be made in any desiredlengths and can be assembled in various shapes and combinations toproduce desired voltage and energy output characteristics. For example,a plurality of such cells can be physically connected to form a largearea web in which thecells are electrically connected in parallel,whereby the magnitude of the power output would indicate the size of afire present in an area adjacent the web.

It is therefore an object of the present invention to provide a thermaldevice for producing electrical energy when heated to within apreselected temperature range.

It is also an object of the present invention to provide such a devicewhich is of rugged and durable construction and which can itself serveas a structural member.

It is another object of the present invention to provide such a devicewhich can be formed into a large number of geometric shapes and whichcan be mechanically and electrically connected with other such devicesinto any desirable pattern with any desirable output characteristic.

It is a further object of the present invention to provide a pluralityof such devices mechanically and electrically connected into a webuseful in the detection of fire.

It is a still further object of the present invention to provide aplurality of such webs so as to provide a three dimensionalrepresentation of a fire.

These an other objects of the present invention will become moreapparent upon reference to the accompanying description and drawings inwhich:

FIG. I is a side elevation, partly in section, of the thermal cell ofthe present invention;

FIG. 2 is a crosssectional view of a thermal battery made up of aplurality of the thermal cells of the present invention;

FIG. 3 is a plan view, partly broken away arid in section of the batteryof FIG. 2;

FIG. 4 is a schematic representation of a web made up of a plurality ofthermal cells;

FIG. 5 is a detailed view of a section of a web of FIG. 4;

FIG. 6 is a view taken along line 6-6 of FIG. 5;

FIG. 7 is a perspective view of the edge connection of the various cellsin the web of FIGS. 4 and 5;

FIG. 8 is a schematic diagram of the electrical circuit of the web ofFIGS. 4 and 5;

FIG. 9 is a representational view of a plurality of webs of thermalcells according to the present invention mounted in an aircraft or othervehicle;

FIG. 10 is a schematic diagram of the electrical circuit of the webs ofFIG. 9; and

FIG. 1 I illustrates the output characteristics of various cellsconstructed in accordance with the teaching of the present invention.

Turning now to FIG. I, the thermal cell I0 of the present invention hasa cylindrical metal core 12, a glass coating 14 disposed on the core anda metal sheath l6 deposited on the glass coating. It has been found thatby using two dissimilar metals and a glass composition that is an ionicconductor in the operating temperature range, useful electric power isgenerated whenthe cell is heated. The materials used for the two metalelectrodes and the glass electrolyte must be selected from those thatwill suitable withstand the expected service temperatures. At the sametime they must provide the necessary electrode potential and a minimizedelectrolyte resistance at the operating temperature to provide usefulpower.

As anode materials, iron and stainless steel have been foundsatisfactory in combination with cathode metals such as silver orcopper. The anode may also be made of iron, chromium, nickel, or hightemperature alloys in which one or more of these metals is a majorconstituent. Since it is possible to use these anode materials as thecore 12, their oxidation resistance does not limit their utility attemperatures up to their melting points. As cathode materials, palladiumand gold as well as silver and copper are useful, as are alloys havingone or more of these metals as a major constituent. The excellentoxidation resistance of the more noble metals of this group, plus therelative ease with which they can be deposited as thin coatings,recommends their use as the outer metal sheath 16.

Two of the more common constituents that satisfy the ionic conductionrequirement are Na i) and K 0. Other oxides of alkali metals, such as LiO, are also contemplated for use. When these are present in the glasselectrolyte in amounts exceeding a few percent. it has been found thatconsiderable electrical energy is generated when the device is heated attemperatures as low as 800 F. A corresponding decrease in theresistivity of the glass electrolyte also occurs at elevatedtemperatures.

Other glass constituents such as B 0 SiO A1 0 TiO ZrO mg. 0, etc. can beused in the fonnulation of tailored glass composition tailored to meetother important criteria, such as a suitable coefficient of thermalexpansion, as will be apparent to those skilled in the art. It has beenfound that the glass composition can be varied to produce a higher poweroutput for short term load applications or a lower, more stable poweroutput for long term load applications. A further effect of varying theglass composition can be to raise or lower the optimum operatingtemperature range or to vary the width of the ranges. Examples of usefulcompositions are:

Example I. A glass having a composition by weight of 30 percent Na O, 30percent B 0 and 40 percent Si0 was coated on a metal core of type 304stainless steel and a sheath of silver was then vapor deposited on theglass coating. The resulting device was found to have an optimumoperating temperature range of l250- 1 575 F.

Example II. A glass having a composition by weight of 30 percent Na tl,30 percent B 0 20 percent Sit) and 20 percent A1 0 was coated on a metalcore of type 304 stainless steel and a sheath of silver was then vapordeposited on the glass coating. The resulting device was found to havean optimum operating temperature range of l450-l575 F.

As can be seen from FIG. 11, these two compositions have quite differentpower output characteristics. Composition I provides a higher initialpower output than does composition II when used with the same electrodecombination; but composition ll produces a greater total energy outputover an extended drain time. FIG. 11 also shows the power outputcharacteristic of a device in which composition II is used with an ironcore or anode and a silver cathode. It can be seen that a large poweroutput can be obtained by making the cell of long length and consequentlarge surface area. Rather than have a single cell of extremely longlength, a plurality of short cells can be suitable stacked and boundtogether, for example, in the manner shown in FIGS. 2 and 3.

In FIGS. 2 and 3, a plurality of cells 10, each having a core 12, aglass coating 14 and a metallic sheath 16 are tightly bun dled togetherby a sheet or sheets of metal foil l8 so that the sheath 16 of each cellis pressed into good electrical contact with the sheaths of theadjoining cells. Each cell is formed so that its metal sheath does notextend to the end of the glass coating, which in turn does not extend tothe end of the central core. The lower ends of the cells are positionedin an insulating cap 20 and then potted in any suitable insulatingmaterial 22 such as a castable ceramic.

A conductive plate 24 is positioned on top of the cells and brazed orsoldered to the cores thereof. An electrode or terminal 26 is solderedto plate 24 and a second insulating cap 28 positioned over the assembly.A second electrode or terminal 30 is suitably connected to the foil 18to serve as a contact to the cell sheaths which as mentioned above aregenerally the cell cathodes. Electrically, this construction results inthe many cells being connected in parallel. It should be obvious tothose skilled in the art that miner modifications can be made in such astructure so that many different electrical seriesparallel connectionsof the cells can be obtained.

As an example of the electrode surface areas obtainable in this type ofassembly, approximately 250,000 cells, each 0.002 inches in diameter,can be stacked in a l inch cube. If the metal core is assumed to be0.001 inch in diameter, the cube will contain almost 800 square inchesof surface area. Using the power output data shown in FIG. II forcomposition ll with a stainless steel core, and assuming that the totalpower output is directly proportional to electrode surface area, it canbe seen that such a 1 inch cube can produce approximately 5.9 watt-hoursover the time period plotted.

Turning now to FIGS. 4, 5, 6 and 7 there is shown a portion of web ormesh constructed ofa plurality of the cells of FIG. I. The cells aremounted on a conductive ring 34 by passing the ends of their metal coresthrough apertures or notches 36, bending them over and spot welding themto the ring (FIG. 7). The ring 34 thus serves as the common anodeconnection or terminal if the metal core of each cell is chosen as theanode. The various cells are interwoven so that their outer metallicsheaths are in close mechanical and good electrical contact at thecrossover points (FIG. 6) so that the cathodes of the cells areconnected together. i

The external cathode connection or terminal may be made to one or moreof the metallic sheaths. The electrical representation of this web isshown in FIG. 8. Each of the batteries 38 is a single cell 10 while eachresistance 40 corresponds to the internal resistance of the cell. All ofthe cells are connected in parallel and the parallel combinationconnected in series with a current limiting resistance 42 and anysuitable extinguishing system or alarm 44.

The web illustrated may be located in any area where there is a firehazard. Since the web can be made to have very little weight, it couldbe made to blanket a large hazard area of, for.

example, a flight vehicle by bonding or otherwise attaching it to thestructure in which the hazard exists without significantly affecting theweight of the vehicle. Only the portion of each cell locatedsufficiently close to a fire to be heated to its operating temperaturewill produce useful power. The portions of the cells in web areasadjacent the hot zone are at lower temperatures and remain relativelyinert. I

This concept is illustrated in FIG. 4 where the web is shown as dividedinto three concentric zones, a central zone A, an intermediate zone Band an outer zone C. Assume that the cells are constructed so that theybegin to produce useful power when heated to 1000 F. If the web isheated by a fire so that the temperature in zone A rises to between l000F. and l600 F useful power will be produced only by the portions of thecells within that zone. In zone B the fire may have raised thetemperature only to between 500 F. and 1000 F and the internalresistance of the glass electrolyte of each cell will be very high andthe power produced by these cell'portions will be negligible. Thetemperature of the portions of the cells in zone C will be even less andthey also will produce negligible power.

The metallic cores in zones B and C remain conductive, however, andserve as insulated leads between the power producing cell portions inzone A and the extinguishing system or alarmllf the fire becomes largeror more intense the cell portions in zones B and C begin to producepower so that the total output increases. The increased output can beused to actuate additional extinguishing devices or further alarms.

A plurality of webs connected electrically in series may be used to givea three dimensional picture of a fire. For example, a web could bemounted on or made a structural part of each of three successivebulkheads 48, 50 and 52 in an aircraft or a ship as shown in FIG. 9, andelectrically connected in series. In FIG. 9, the bulkheads 48, 50 and 52are provided with insulating strips 54, 56 and 58 respectively, eachstrip having a conductive strip 60 mounted thereon to which the webs 62,64 and 66 are fastened by welding or the like. The webs are connected ina series circuit with suitable indicators by the conductors 68, 70, 72and 74. The electrical schematic diagram of this arrangement is shown inFIG. 10. If a fire begins adjacent the central bulkhead 50, the web 64mounted thereon would be heated and produce an energy outputcorresponding to this area. If thefire spread to the areas adjoiningbulkheads 48 and 52, the webs 62 and 66 also begin to produce an output.Thus, the total energy produced reflects the web area heated while thevoltage generated as a result of the web series connection indicates thedepth of the fire.

From the foregoing description, it can be seen that a thermallyactivated cell has been provided in the shape of a fiber orfilament,that is simple in construction, rugged, and capable of producing arelatively large power output and yet can be made very compact andlightweight. If desired, it can also be constructed to add strength tothe structure in which it is incorporated. The cell is particularlyuseful when combined with others to form a fire hazard detector becauseit is essentially foolproof and can produce sufficient power to actuatean extinguishing or alarm device. It should be understood that thevarious combinations, both mechanical and electrical, shown anddescribed are illustrative only and many other useful combinations willoccur to those skilled in the art The invention may be embodied in otherspecific forms not departing from the spirit or central characteristicsthereof. The present embodiments are therefore to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription, and all changes which come' within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

I claim:

l, A web for use in detecting fires of other high temperature conditionscomprising: aconductive supporting ring, a plurality of filamentarythermal cells mounted on said supporting ring, each of said cellscomprising an elongated core comprising an electricallyconductive'metal, stainless steel, a glass coating having thecomposition 30 percent Na 0, 30 percent B 03, 20 Si0 and 20 percent N 0disposed on said core, said glas's coating being ionically conductivewhen heated to within a preselected temperature range and a sheathdisposed on said glass coating, said sheath comprising an electricallyconductive metal, silver, dissimilar to said core metal, a first groupof said cells being arranged in parallel within said ring and havingeach end of the cores thereof fastened to said ring, a second group ofsaid cells being arranged in parallel within said ring and having eachend of the cores thereof fastened to said ring, the cells of said secondgroup being displaced approximately from the cells of said first groupand interwoven therewith so that the sheaths of the cells of the firstgroup engage and make good electrical contact with the sheaths of thecells of the second group at the points of intersection therewith.

2. A web for use in detecting fires or other high temperature conditionscomprising: a conductive supporting ring, a plurality of filamentarythermal cells mounted on said supporting ring, each of said cellscomprising an elongated core comprising an electrically conductivemetal, stainless steel, a glass coating having the composition 30percent Na,0, 30 percent 8 0 and 40 percent Si0, disposed on said core,said glass coating being ionically conductive when heated to within apreselected temperature range and a sheath disposed on said glasscoating, said sheath comprising an electrically conductive metal,silver, dissimilar to said core metal, a first group of

1. A web for use in detecting fires of other high temperature conditionscomprising: a conductive supporting ring, a plurality of filamentarythermal cells mounted on said supporting ring, each of said cellscomprising an elongated core comprising an electrically conductivemetal, stainless steel, a glass coating having the composition 30percent Na20, 30 percent B203, 20 Si02 and 20 percent N203 disposed onsaid core, said glass coating being ionically conductive when heated towithin a preselected temperature range and a sheath disposed on saidglass coating, said sheath comprising an electrically conductive metal,silver, dissimilar to said core metal, a first group of said cells beingarranged in parallel within said ring and having each end of the coresthereof fastened to said ring, a second group of said cells beingarranged in parallel within said ring and having each end of the coresthereof fastened to said ring, the cells of said second group beingdisplaced approximately 90* from the cells of said first group andinterwoven therewith so that the sheaths of the cells of the first groupengage and make good electrical contact with the sheaths of the cells ofthe second group at the points of intersection therewith.
 2. A web foruse in detecting fires or other high temperature conditions comprising:a conductive supporting ring, a plurality of filamentary thermal cellsmounted on said supporting ring, each of said cells comprising anelongated core comprising an electrically conductive metal, stainlesssteel, a glass coating having the composition 30 percent Na2O, 30percent B203 and 40 percent Si02 disposed on said core, said glasscoating being ionically conductive when heated to within a preselectedtemperature range and a sheath disposed on said glass coating, saidsheath comprising an electrically conductive metal, silver, dissimilarto said core metal, a first group of said cells being arranged inparallel within said ring and having each end of the cores thereoffastened to said ring, a second group of said cells being arranged inparallel within said ring and having each end of the cores thereoffastened to said ring, the cells of said second group being displacedapproximateLy 90* from the cells of said first group and interwoventherewith so that the sheaths of the cells of the first group engage andmake good electrical contact with the sheaths of the cells of the secondgroup at the points of intersection therewith.